Even-electron ligand

As a rule, complexes with even-electron ligands, such as solvates, alkene, benzene complexes, do not produce survivor ions. This may be reversed, however, by changing the experimental conditions (target gas, experimental time frame, etc.). Sometimes, adding a ligand increases the stability of complexes. For example, neutral LFeCO showed an unexpectedly higher stability compared with FeL. ... 

Elements beyond the second row of the periodic table can form bonds to more than four ligands and can be associated with more than an octet of electrons. These features are possible for two reasons. First, elements with > 2 have atomic radii that are large enough to bond to 5, 6, or even more ligands. Second, elements with > 2 have d orbitals whose energies are close to the energies of the valence p orbitals. An orbital overlap description of the bonding in these species relies on the participation of d orbitals of the inner atom. 

As base B several electron donors can be employed, e.g. amines 127), hydrazines128), amine oxides129, ethers126, phosphanes 130>131, and even charged ligands such as halogen anions 126) and many others 126). There may be formed either 1 1 or 1 2 adducts as in Eq. (7), an equilibrium being assumed to be established between these two adducts ... 

Rearrangements involving hydrogen transfer, either within the ligand or to the metal, have been discussed extensively by Muller (13) and Chambers et al. (3). These include main group elements for which alkene elimination from even-electron alkyl-containing ions. 

For the synthesis of bidentate ligands, supramolecular approaches have led to a renaissance in homogeneous catalyst discovery (Chapters 2, 4, 8, 9,10), and in a few cases even monodentate ligands have been modified in a supramolecular fashion (Chapter 8, Section 8.2). Combinations of monodentate ligands can be left to chance and in several instances this has led to successful, new catalysts [96]. Such heterocombinations can form spontaneously for steric or electronic reasons or the reactivity of the combinations can be different such that on certain occasions highly enantioselective catalysts are obtained. There are many ways to synthesize the desired heterocombinations selectively and the ionic modification outlined in Section 10.4 is only one of them since nitration (followed by reduction to amines) and sulfonation are robust methods, the ionic route may prove useful. Hydrogen bonding between different donor-acceptors (Chapters 2 and 8), Lewis add-base interactions (Chapter... 

Mn X bond, and X is regarded as a one-electron ligand even if it is a halogen. 

TT-Bonded ligands can be closed shell, 2n electron donors (n = 1 — 3) such as alkenes, allenes, alkynes, arenes, and polyenes these have been termed even polyene ligands. They may also be open shell, odd polyene ligands such as allyl, pentadienyl, cyclopropenyl, and cyclopentadienyl, which are formally viewed as anionic hgands, donating 2n electrons (n = 1 - 3). 

Another method for determining total electron count treats odd-electron donor ligands (alkyl, Cp, etc.) as anionic, even-electron donors. The number of electrons contributed by the metal is calculated from the metal s oxidation state. Both methods give the same answer for total electron count. 

Heck reaction. Solvent-free conditions with microwave irradiation have been developed for the Heck reaction. Phosphites are excellent ligands such that even electron-deficient aryl chlorides can be used to couple with different alkenes. Isoquinolines are formed by using the more conventional procedure note the same 3-(o-iodobenzylamino)acrylic esters give dihydroisoindole derivatives when they are exposed to Bu,SnH-AIBN. A combination of BUjP and dppp together with /-Pr NEt constitutes support for Pd(OAc)2 in an intramolecular coupling which leads to benzophenanthridines. ... 

Diphosphorus ligands stemming from P4 activation are usually quenched in multinuclear complexes, where they generally adopt the side-on coordination mode. As mentioned in the mechanistic section, multinuclear diphosphorus complexes coordinated to 15 VE metal fragments may form via dimerization of reactive P, intermediates and are incorporated into dimetalla-diphosphorus tetrahedranes. However, when P2-complexes are derived from the direct reaction of even-electron metal precursors and P4, it is likely that they form from the... 

Cyclopropane systems can be bound to transition-metal centers either through even-numbered electron rt-bonds within the ligand (alkene, diene, alkyne) or as odd-numbered electron ligands (alkyl, allyl, dienyl). According to the bonding type, different methods of decomplexation are applied. Cyclopropane systems attached to the metal through hetero functions as n-donors are not discussed here. 

Decomplexation of organic ligands bound to the metal in the odd numbered 7 or fashion (alkyl, allyl or dienyl complexes and others) is usually accompanied by formation of new (T-bonds (C-H, C-C, C — Heteroatom) depending on the reaction conditions applied. The ligand cannot be decomplexed unchanged as possible with even-numbered electron ligands, such as alkenes, dienes or alkynes. 

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